Top coat material and use thereof in lithography processes

ABSTRACT

A top coat material for applying on top of a photoresist material is disclosed. The top coat material includes a polymer, which includes at least one fluorosulfonamide monomer unit having one of the following two structures:  
                 
 
wherein: M is a polymerizable backbone moiety; Z is a linking moiety selected from the group consisting of —C(O)O—, —C(O)—, —OC(O)—, and —O—C(O)—C(O)—O—; R 1  is selected from the group consisting of an alkylene, an arylene, a semi- or perfluorinated alkylene, and a semi- or perfluorinated arylene; p and q are 0 or 1; R 2  is selected from the group consisting of hydrogen, fluorine, an alkyl group of 1 to 6 carbons, and a semi- or perfluorinated alkyl group of 1 to 6 carbons; n is an integer from 1 to 6; and R 3  is selected from the group consisting of hydrogen, an alkyl, an aryl, a semi- or perfluorinated alkyl, and a semi- or perfluorinated aryl. The top coat material may be used in lithography processes, wherein the top coat material is applied on a photoresist layer. The top coat material is preferably soluble in aqueous alkaline developer. The top coat material is also preferably insoluble in water, and is therefore particularly useful in immersion lithography techniques using water as the imaging medium.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a top coat material and the use thereof inlithography processes. More particularly, this invention is directed toa top coat material which is easy to apply, insoluble in water butsoluble in developer, therefore can be removed in the develop stage.This top coat may be especially useful for immersion lithography inwhich a liquid such as water is used as the exposure medium between thelens fixture of an exposure tool and the photoresist-coated wafer.

2. Description of the Related Art

Traditionally, top coat materials have been used in photolithography asanti-reflective films on the top of a photoresist. The topanti-reflective coat (TARC) materials can prevent the multipleinterference of light that takes place within the photoresist layerduring exposure. As a result, the critical dimension (CD) variation ofthe geometrical features of a photoresist pattern that is caused by thevariation in the thickness of the photoresist film can be minimized.

To fully take advantage of the anti-reflective effect of the top coat,the refractive index of the top coat material (n_(t)) should be at aboutthe square root of the multiplication of the refractive index of theexposure medium (n_(m)) and the refractive index of the underlyingphotoresist (n_(r)). If the exposure medium is air, as in the case for“dry” lithography, the optimal refractive index of the top coat material(n_(t)) should be at about the square root of the refractive index ofthe underlying photoresist (n_(r)) because the refractive index of airis roughly 1.

For ease of processing, classic TARC materials are designed to besoluble in both water and aqueous base developer so that they can beapplied directly from water solution and subsequently removed by theaqueous base developer during the develop stage.

Numerous top coat materials have been developed to meet these tworequirements of optimal refractive index and solubility. For example,U.S. Pat. Nos. 5,744,537 and 6,057,080 disclose aqueous-soluble TARCmaterials comprising a polymeric binder and a fluorocarbon compound, andwhich have nearly ideal refractive indexes on the order of 1.3-1.4. U.S.Pat. No. 5,879,853 also disclose a TARC material that is removable by awet process. U.S. Pat. No. 5,595,861 similarly discloses a TARCcomprising partially fluorinated compounds, which can also be watersoluble. U.S. Pat. No. 6,274,295 discloses a TARC material comprising alight absorbing compound having a wavelength of maximum absorptionhigher than an exposure wavelength used to expose the photoresist. ThisTARC can also be water-soluble. Finally, U.S. Pat. No. 5,240,812discloses a protective material for use as an overcoat film for acidcatalyzed resist composition to prevent contamination from vapors oforganic and inorganic bases. While not specifically disclosed as being aTARC, the overcoat can also be water soluble.

Immersion lithography offers the potential to extend the use of opticallithography to print smaller features. In immersion lithography, air isreplaced by a liquid medium such as water between the lens and thewafer. Use of a medium with an index of refraction higher than airresults in a greater numerical aperature (NA), and therefore allowsprinting of smaller features. See “Technology Backgrounder: ImmersionLithography,” published by ICKnowledge.com athttp://www.icknowledge.com, May 28, 2003. See also L. Geppert, “ChipMaking's Wet New World,” IEEE Spectrum, Vol. 41, Issue 5, May 2004, pp.29-33.

For liquid immersion lithography, a top coat material can be used inbetween the exposure medium and the resist-coated wafer to preventphotoresist components from leaching into the immersion medium. A topcoat material can also prevent the permeation of the exposure mediuminto the photoresist film. One of the requirements for the top coatmaterial, of course, is its insolubility in the exposure medium.Preferably, the top coat material can also act as a TARC layer.

Water has been proposed as the exposure medium for 193 nm immersionlithography. Therefore, classic water-soluble TARC materials such asthose described above can not be used as top coats for 193 nm immersionlithography. Moreover, since water has higher refractive index (1.47 at193 nm) than air (˜1 at 193 nm), the optimal refractive index for TARCmaterials used for 193 nm immersion lithography is also higher than thatof classic TARCs.

Thus, there remains a need for a top coat material that is insoluble inwater but soluble in aqueous base developer, and also has desiredoptical properties so that it can also be used as a TARC.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a top coat materialfor applying on top of a photoresist material. The top coat materialcomprises a polymer, which comprises at least one fluorosulfonamidemonomer unit having one of the following two structures:

wherein: M is a polymerizable backbone moiety; Z is a linking moietyselected from the group consisting of —C(O)O—, —C(O)—, —OC(O)—, and—O—C(O)—C(O)—O—; R₁ is selected from the group consisting of analkylene, an arylene, a semi- or perfluorinated alkylene, and a semi- orperfluorinated arylene; p and q are 0 or 1; R₂ is selected from thegroup consisting of hydrogen, fluorine, an alkyl group of 1 to 6carbons, and a semi- or perfluorinated alkyl group of 1 to 6 carbons; nis an integer from 1 to 6; and R₃ is selected from the group consistingof hydrogen, an alkyl, an aryl, a semi- or perfluorinated alkyl, and asemi- or perfluorinated aryl.

In another aspect, the invention is directed to a method of forming apatterned material layer on a substrate, the method comprising:providing a substrate having a material layer on a surface thereof,depositing a photoresist composition on the substrate to form aphotoresist layer on the material; applying the top coat materialmentioned above on the photoresist layer, thereby forming a coatedsubstrate; patternwise exposing the coated substrate to imagingirradiation; contacting the coated substrate with an aqueous alkalinedeveloper, wherein the top coat material and a portion of thephotoresist layer are simultaneously removed from the coated substrate,thereby forming a patterned photoresist layer on the material layer; andtransferring the pattern in the photoresist layer to the material layer.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a top coat material comprising apolymer which comprises a repeating unit with a fluorosulfonamidestructure. The top coat is preferably insoluble in water but soluble inaqueous base developer so that it can be used for 193 nm immersionlithography. Additionally, the top coat material of the presentinvention can be adjusted to act as a TARC so that better processcontrol of image formation can be achieved. For 193 nm immersionlithography using water as the exposure medium, the optimal refractiveindex for a TARC material is about 1.5 to 1.7.

The invention is specifically directed to a top coat material comprisinga polymer which comprises at least one fluorosulfonamide monomer unitpreferably having one of the following two structures:

wherein: M is a polymerizable backbone moiety; Z is a linking moietyselected from the group consisting of —C(O)O—, —C(O)—, —OC(O)—, and—O—C(O)—C(O)—O—; R₁ represents one of an alkylene, an arylene, a semi-or perfluorinated alkylene, and a semi- or perfluorinated arylene; p andq are 0 or 1; R₂ represents one of hydrogen, fluorine, an alkyl group of1 to 6 carbons, and a semi- or perfluorinated alkyl group of 1 to 6carbons; n is an integer from 1 to 6; and R₃ represents one of hydrogen,an alkyl, an aryl, a semi- or perfluorinated alkyl, and a semi- orperfluorinated aryl.

Examples of the polymerizable backbone moiety, M, include:

where R₄ represents hydrogen, an alkyl group of 1 to 20 carbons, a semi-or perfluorinated alkyl group of 1 to 20 carbons, or CN; and

where t is an integer from 0 to 3.

In exemplary embodiments of the present invention, the fluorosulfonamidemonomer unit may include, but is not limited to:

The polymer of the top coat material may further comprise at least oneco-monomer unit to permit further regulation of, for example,dissolution properties and thermal properties in exemplary embodiments.Examples of such co-monomer units include, but are not limited to:

The top coat material may further comprise at least one solvent which ispreferably immiscible with the underlying photoresist material. Suitablesolvents include, but are not limited to: 1-butanol, methanol, ethanol,1-propanol, ethylene glycol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, 1,2-propanediol, and 1,3-propanediol.

The top coat material of the invention is preferably insoluble in waterbut is soluble in aqueous base developer. Moreover, the top coatmaterial is preferably substantially optically transparent to theexposure radiation for the underlying photoresist material, to allowpatterning of the photoresist material.

It is also preferable that the top coat material have a refractive indexin the range of about 1.2 to 1.8. For 193 nm immersion lithography usingwater as the exposure medium, the refractive index of the top coatmaterial is most preferably in the range of about 1.5 to 1.7.

In another aspect of the invention, the top coat material may be used ina method of forming a patterned material layer on a substrate. Thematerial layer may be, for example, a ceramic, dielectric, metal orsemiconductor layer, such as those used in the manufacture of highperformance integrated circuit devices and associated chip carrierpackages. In the method, a photoresist composition is first deposited onthe substrate by known means, to form a photoresist layer on thematerial. The substrate with the resist layer then may be baked(pre-exposure bake) to remove any solvent from the photoresistcomposition and improve the coherence of the resist layer. Typicalpre-exposure baking temperature is about 80 to about 150° C. Typicalresist thickness is about 100 to about 500 nm. Any suitable resistcomposition may be used, such as the resist composition disclosed inU.S. Pat. Nos. 6,534,239 and 6,635,401 B2, and U.S. patent applicationSer. No. 10/663,553, filed Sep. 16, 2003, the disclosures of which areincorporated herein by reference.

Next, the top coat material of the invention is applied on thephotoresist layer, thereby forming a coated substrate. The coatedsubstrate is then exposed to an appropriate irradiation source, througha patterned mask. In one exemplary embodiment, the imaging radiation is193 nm radiation. In another embodiment, the imaging radiation is 157 nmradiation. In another embodiment, the imaging radiation is 248 nmradiation. The coated substrate also may be exposed to such imagingradiation using immersion lithography, wherein an imaging medium isapplied to the coated substrate prior to exposure. In a preferredembodiment, the imaging medium is water.

The coated substrate is then contacted with an aqueous base developer,such as 0.263 N tetramethyl ammonium hydroxide, thereby removing the topcoat material and a portion of the photoresist layer simultaneously fromthe coated substrate. Contact with developer forms a patternedphotoresist layer on the material layer.

The pattern in the photoresist layer then may be transferred to thematerial layer on the underlying substrate. Typically, the transfer isachieved by reactive ion etching or some other etching technique. Themethod of the invention may be used to create patterned material layerstructures such as metal wiring lines, holes for contacts or vias,insulation sections (e.g., damascene trenches or shallow trenchisolation), trenches for capacitor structures, etc. as might be used inthe design of integrated circuit devices.

The processes to making these (ceramic, dielectric, metal orsemiconductor) features generally involve providing a material layer orsection of the substrate to be patterned, applying a layer of resistover the material layer or section, applying a top coat layer on thelayer of resist, patternwise exposing the top coat and resist layers toradiation, developing the pattern by contacting the exposed top coat andresist with a developer, etching the layer(s) underlying the resistlayer at spaces in the pattern whereby a patterned material layer orsubstrate is formed, and removing any remaining resist from thesubstrate. In some instances, a hard mask may be used below the resistlayer to facilitate transfer of the pattern to a further underlyingmaterial layer or section. It should be understood that the invention isnot limited to any specific lithography technique or device structure.

The following non-limiting examples are provided to further illustratethe present invention. Because these examples are provided forillustrative purposes only, the invention embodied therein should belimited thereto.

EXAMPLE 1 Synthesis of poly(2-trifluoromethanesulfonylaminoethylmethacrylate) (poly(I))

A solution of 7.8 g (0.03 mol) of 2-trifluoromethanesulfonylaminoethylmethacrylate (I) and 0.061 g (0.0003 mol) dodecanethiol in 22.6 g of2-butanone was first prepared. To this solution was added 0.148 g(0.0009 mol) of 2,2′-azobisisobutyronitrile (AIBN). The solution wasdeoxygenated by bubbling dry N₂ for 0.5 hr and then allowed to refluxfor 12 hr. The reaction mixture was cooled to room temperature andprecipitated in 400 ml of hexanes with rigorous stirring. The resultingwhite solid was collected by filtration, washed with several portions ofhexanes and dried under vacuum at 60° C. for 20 hr.

EXAMPLE 2 Synthesis of poly(I-co-XVIII)

A solution of 4.7 g (0.018 mol) of 2-trifluoromethanesulfonylaminoethylmethacrylate (I), 2.83 g (0.012 mol) hydroxyadamantyl methacrylate(XVIII) and 0.061 g (0.0003 mol) dodecanethiol in 22.6 g of 2-butanonewas first prepared. To this solution was added 0.148 g (0.0009 mol) ofAIBN. The solution was deoxygenated by bubbling dry N₂ for 0.5 hr andthen allowed to reflux for 12 hr. The reaction mixture was cooled toroom temperature and precipitated in 400 ml of hexanes with rigorousstirring. The resulting white solid was collected by filtration, washedwith several portions of hexanes and dried under vacuum at 60° C. for 20hr.

EXAMPLE 3 Synthesis of poly(1-co-XVIII-co-XVI)

A solution of 5.22 g (0.02 mol) of 2-trifluoromethanesulfonylaminoethylmethacrylate (I), 3.78 g (0.016 mol) hydroxyadamantyl methacrylate(XVIII), 0.52 g (0.004 mol) 2-hydroxyethyl methacrylate (XVI), and 0.081g (0.0004 mol) dodecanethiol in 22.6 g of 2-butanone was first prepared.To this solution was added 0.197 g (0.0012 mol) of AIBN. The solutionwas deoxygenated by bubbling dry N₂ for 0.5 hr and then allowed toreflux for 12 hr. The reaction mixture was cooled to room temperatureand precipitated in 400 ml of hexanes with rigorous stirring. Theresulting white solid was collected by filtration, washed with severalportions of hexanes and dried under vacuum at 60° C. for 20 hr.

EXAMPLE 4 Synthesis of poly(1-co-VIII-co-XVIII-co-XVI)

A solution of 2.35 g (0.009 mol) of 2-trifluoromethanesulfonylaminoethylmethacrylate (I), 1.53 g (0.009 mol) 2-methacryloyl-γ-butyrolactone(VIII), 2.12 g (0.009 mol) hydroxyadamantyl methacrylate (XVIII), 0.39 g(0.003 mol) 2-hydroxyethyl methacrylate (XVI), and 0.182 g (0.0009 mol)dodecanethiol in 22.6 g of 2-butanone was first prepared. To thissolution was added 0.246 g (0.0015 mol) of AIBN. The solution wasdeoxygenated by bubbling dry N₂ for 0.5 hr and then allowed to refluxfor 12 hr. The reaction mixture was cooled to room temperature andprecipitated in 400 ml of hexanes with rigorous stirring. The resultingwhite solid was collected by filtration, washed with several portions ofhexanes and dried under vacuum at 60° C. for 20 hr.

EXAMPLE 5 Synthesis of poly(trifluoromethanesulfonylaminomethylnorbornene) (poly(III))

A homopolymer of trifluoromethanesulfonylaminomethyl norbornene (III)was prepared by addition polymerization.

EXAMPLE 6 Lithographic Evaluation

For the purpose of evaluative lithographic experiments, a top coatmaterial containing the polymer prepared in Example 5 (3% by weight) and1-butanol (97% by weight) was prepared. The top coat material wasapplied over a photoresist (AMX1741, from JSR) coated wafer. The filmswere baked at 110° C. for 60 seconds. The thickness of the top coat was˜50 nm.

The following water solubility test was then conducted. The coatedsubstrate was immersed in water for 2 minutes. Thickness measured beforeand after immersion confirmed that there was no thickness loss of thetop coat material in water.

The above coated wafer was then exposed with 0.75 NA lithography toolusing 193 nm radiation. As a comparison, a wafer coated with AMX1741photoresist without the top coat material was also exposed at the sametime. Both wafers were able to resolve L/S (line/space) pairs down to 90nm 1:1 L/S. The wafer with the top coat showed improved profiles andexposure latitude over the one without top coat.

Thickness measurement before and after develop confirmed that the topcoat material was completely removed during develop stage. In the meantime, no additional thickness loss was observed in the unexposed areawith the use of the top coat.

While the present invention has been particularly described inconjunction with a specific preferred embodiment and other alternativeembodiments, it is evident that numerous alternatives, modifications andvariations will be apparent to those skilled in the art in light of theforegoing description. It is therefore intended that the appended claimsembrace all such alternatives, modifications and variations as fallingwithin the true scope and spirit of the present invention.

1. A top coat material for applying on top of a photoresist material,the top coat material comprising a polymer, said polymer comprising atleast one fluorosulfonamide monomer unit having one of the following twostructures:

wherein: M is a polymerizable backbone moiety; Z is a linking moietyselected from the group consisting of —C(O)O—, —C(O)—, —OC(O)—, and—O—C(O)—C(O)—O—; R₁ is selected from the group consisting of analkylene, an arylene, a semi- or perfluorinated alkylene, and a semi- orperfluorinated arylene; p and q are 0 or 1; R₂ is selected from thegroup consisting of hydrogen, fluorine, an alkyl group of 1 to 6carbons, and a semi- or perfluorinated alkyl group of 1 to 6 carbons; nis an integer from 1 to 6; and R₃ is selected from the group consistingof hydrogen, an alkyl, an aryl, a semi- or perfluorinated alkyl, and asemi- or perfluorinated aryl.
 2. The top coat material of claim 1,wherein M is a polymerizable backbone moiety having one of the followingtwo structures:

wherein: R₄ is selected from the group consisting of hydrogen, an alkylgroup of 1 to 20 carbons, a semi- or perfluorinated alkyl group of 1 to20 carbons, and CN; and t is an integer from 0 to
 3. 3. The top coatmaterial of claim 1, further comprising at least one solvent which isimmiscible with the photoresist material.
 4. The top coat material ofclaim 3, wherein the solvent is selected from the group consisting of1-butanol, methanol, ethanol, 1-propanol, ethylene glycol,1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-propanediol, and1,3-propanediol.
 5. The top coat material of claim 1, wherein the topcoat material is insoluble in water.
 6. The top coat material of claim5, wherein the top coat material is soluble in aqueous alkalinedeveloper.
 7. The top coat material of claim 1, wherein the top coatmaterial is substantially optically transparent to the exposureradiation for the underlying photoresist material.
 8. The top coatmaterial of claim 1, wherein the top coat material has a refractiveindex in the range of about 1.2 to 1.8.
 9. The top coat material ofclaim 1, wherein the top coat material has a refractive index in therange of about 1.5 to 1.7.
 10. The top coat material of claim 1, whereinthe fluorosulfonamide monomer unit is selected from the group consistingof:


11. The top coat material of claim 1, wherein the polymer furthercomprises a co-monomer unit selected from the group consisting of:


12. A top coat material for applying on top of a photoresist material,the top coat material a polymer, said polymer comprising at least onefluorosulfonamide monomer unit having one of the following twostructures:

wherein: M is a polymerizable backbone moiety; Z is a linking moietyselected from the group consisting of —C(O)O—, —C(O)—, —OC(O)—, and—O—C(O)—C(O)—O—; R₁ is selected from the group consisting of analkylene, an arylene, a semi- or perfluorinated alkylene, and a semi- orperfluorinated arylene; p and q are 0 or 1; R₂ is selected from thegroup consisting of hydrogen, fluorine, an alkyl group of 1 to 6carbons, and a semi- or perfluorinated alkyl group of 1 to 6 carbons; nis an integer from 1 to 6; and R₃ is selected from the group consistingof hydrogen, an alkyl, an aryl, a semi- or perfluorinated alkyl, and asemi- or perfluorinated aryl, and M is a polymerizable backbone moietyhaving one of the following two structures:

wherein: R₄ is selected from the group consisting of hydrogen, an alkylgroup of 1 to 20 carbons, a semi- or perfluorinated alkyl group of 1 to20 carbons, and CN; and t is an integer from 0 to
 3. 13. The top coatmaterial of claim 12, further comprising a solvent which is immisciblewith the photoresist material.
 14. The top coat material of claim 12,wherein the solvent is selected from the group consisting of 1-butanol,methanol, ethanol, 1-propanol, ethylene glycol, 1,2-butanediol,1,3-butanediol, 1,4-butanediol, 1,2-propanediol, and 1,3-propanediol.15. The top coat material of claim 12, wherein the top coat material isinsoluble in water.
 16. The top coat material of claim 15, wherein thetop coat material is soluble in aqueous alkaline developer.
 17. The topcoat material of claim 12, wherein the top coat material issubstantially optically transparent to the exposure radiation for theunderlying photoresist material.
 18. The top coat material of claim 12,wherein the top coat material has a refractive index in the range ofabout 1.2 to 1.8.
 19. The top coat material of claim 12, wherein the topcoat material has a refractive index in the range of about 1.5 to 1.7.